A cacophony of feedback howls, odd keyboard blasts and tasty-lick guitar noodles of every conceivable rock genre echoes through the halls of NoHo's AMP studios. A burst of melodic brass from behind a door at the end of a corridor pierces the discord. It's the sound of the rehearsal stage where Troubadour Theater Company musical director Eric Heinly has spent three weeks re-creating the mellifluous sound of early-'70s rock balladeers Chicago for the Troubies' newest musical comedy mash-up, The Two Gentlemen of Chicago.

Inside the living room–sized space, a seven-piece band tunes up as the arriving Troubies squeeze into what's left of the studio. Tonight they're working with the band for the first time, trying out the retrofitted lyrics director Matt Walker has written for his Shakespeare parody.

Soon Walker arrives, sporting a baseball cap and several weeks' worth of beard stubble. Company veteran Lisa Valenzuela grabs a mic and the band cranks up with "25 or 6 to 4." Heinly has done his homework: It sounds exactly like vintage Chicago. As the cast members take their turn with the band, individual actors trickle back out into the hallway to talk about just how they go about devising the Troubies' brand of family-friendly but boundary-pushing comedy

Matthew Morgan explains that up to half of each show comes out of company improvs, clowning and joke-tweaking contributed by the actors themselves. For instance, in Two Gentlemen, he has a scene with Beth Kennedy that's a kind of "Who's on first?" bit but in Shakespearean language, but it evolved even further to heighten the comedy. "We could do that here and there'd just be stunned silence," he says. "So Matt came in with a great little [bit] of wordplay that's very contemporary, and we played that scene [with Beth] asking the questions and I'm the one giving the answers, and the scene just sort of ends. But then Beth and I found that there was some fun to sort of add to it and create more, but doing it the other way ... me becoming the one who asks the questions and her having the answers."

Onstage, Walker performs as both actor and company ringmaster, frequently bushwhacking his unflappable cast with surprise ad libs, or stopping the show in midscene to mercilessly haze a late-arriving audience member. His flawlessly timed improvisations torque every Troubie performance with the comic tension of the unexpected.

To Rob Nagle, they also gave the impression that Walker's is an auteurist enterprise. Then Nagle joined the company. "Yes, he's the leader," Nagle says, "and comes in with an adaptation to start with — he does all the heavy lifting. But then once you're in rehearsals ... it's much more collaborative than I ever thought."

Walker doesn't encourage his performers to collaborate. He insists. "I've done a lot of other theater," veteran Kennedy says. "This is much more unconventional. We're always writing."

She shows me her script. Every available margin is filled with what looks like the mad scrawl of a paranoid schizophrenic. "In my car with my voice recorder. As I'm sitting waiting to go onstage or I'm onstage."

An actor will jump in during rehearsal and tell her, "BK, why don't you do this?" "It'll interrupt the scene — 'Oh my God, I have a great idea,' " she says. "It's not super sacred here." —Bill Raden